[PATCH] fs/9p: fix uninitialized values during inode evict

[Eric Van Hensbergen]

If an iget fails due to not being able to retrieve information
from the server then the inode structure is only partially
initialized.  When the inode gets evicted, references to
uninitialized structures (like fscache cookies) were being
made.

This patch checks for a bad_inode before doing anything other
than clearing the inode from the cache.  Since the inode is
bad, it shouldn't have any state associated with it that needs
to be written back (and there really isn't a way to complete
those anyways).

Reported-by: syzbot+eb83fe1cce5833cd66a0@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Eric Van Hensbergen <ericvh@xxxxxxxxxx>
---
 fs/9p/vfs_inode.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/fs/9p/vfs_inode.c b/fs/9p/vfs_inode.c
index 360a5304ec03..b01b1bbf2493 100644
--- a/fs/9p/vfs_inode.c
+++ b/fs/9p/vfs_inode.c
@@ -344,17 +344,21 @@ void v9fs_evict_inode(struct inode *inode)
 	struct v9fs_inode __maybe_unused *v9inode = V9FS_I(inode);
 	__le32 __maybe_unused version;
 
-	truncate_inode_pages_final(&inode->i_data);
+	if (!is_bad_inode(inode)) {
+		truncate_inode_pages_final(&inode->i_data);
 
-	version = cpu_to_le32(v9inode->qid.version);
-	netfs_clear_inode_writeback(inode, &version);
+		version = cpu_to_le32(v9inode->qid.version);
+		netfs_clear_inode_writeback(inode, &version);
 
-	clear_inode(inode);
-	filemap_fdatawrite(&inode->i_data);
+		clear_inode(inode);
+		filemap_fdatawrite(&inode->i_data);
 
 #ifdef CONFIG_9P_FSCACHE
-	fscache_relinquish_cookie(v9fs_inode_cookie(v9inode), false);
+		if (v9fs_inode_cookie(v9inode))
+			fscache_relinquish_cookie(v9fs_inode_cookie(v9inode), false);
 #endif
+	} else
+		clear_inode(inode);
 }
 
 struct inode *v9fs_fid_iget(struct super_block *sb, struct p9_fid *fid)

---
base-commit: acade3ac5c19d3e1a6e4934ab250b192dc787675
change-id: 20240319-fix-evict-uninitialized-value-a7a401492199

Best regards,
-- 
Eric Van Hensbergen <ericvh@xxxxxxxxxx>